Hundreds of Syrians have fled the coastal town of Baniyas where activists claim that fighters loyal to the president, Bashar al-Assad, have carried out a massacre.

Sunni Muslim families left on Saturday, fearing further sectarian violence after more than 100 people were killed overnight by pro-Assad militias, according to the Syrian Observatory for Human Rights.

The pro-opposition monitoring group said 62 bodies had been identified so far, including 14 children. It posted a video online showing the bodies of 10 people – half of them children – who it said had been killed in the Ras al-Nabaa quarter of the town. Some were lying in pools of blood, and one toddler was covered in burns, her clothes singed and her legs charred.

Another video posted online showed what activists said were the bodies of 20 people killed in Banias overnight, all from the same family, including women and nine children.

"I estimate that hundreds of families left and headed for nearby towns like Jableh and Tartous," said Rami Abdelrahman, head of the British-based Observatory.

"But now the army is turning people back at the checkpoints outside the town, telling them to go back to Baniyas, that nothing is wrong. There are also announcements going out on mosque loudspeakers telling people to return home."

The reports and videos could not be independently verified as the Syrian government restricts access for independent media.

The Observatory blamed the killings on the National Defence Forces, a new paramilitary group made up mostly of fighters from minorities who back Assad.

"The United States is appalled by horrific reports that more than 100 people were killed May 2 in gruesome attacks on the coastal town of Baida," the US state department said in a statement.

"As the Assad regime's violence against innocent civilians escalates, we will not lose sight of the men, women, and children whose lives are being so brutally cut short. We call on all responsible actors in Syria to speak out against the perpetration of unlawful killings against any group, regardless of faith or ethnicity."

The Syrian conflict, now in its third year, started with largely peaceful protests against Assad's rule in March 2011, but shifted into an armed insurgency as opposition supporters took up weapons to fight a harsh regime crackdown on dissent.

The conflict has devastated the country, killing more than 70,000 people, forcing more than a million Syrians to seek refuge in neighbouring countries such as Jordan, Lebanon and Turkey, and displacing millions more inside Syria.